The present invention relates generally to golf clubs and, more particularly, to the heads of iron-type golf clubs.
Among the varied clubs that a golfer must master, or at least become competent in using, are so-called short irons. A special category of short irons are wedges. The types of wedges a golfer may have in his or her bag include an approach, pitching, sand, and/or lob wedge. Each type of wedge has a range of loft angles associated with it, ranging overall from about 45 degrees to about 61 degrees. This provides in a high launch angle, with the golf ball typically obtaining a high spin rate.
A wedge is used to hit the ball onto the green from a location relatively close to the green, and sometimes from a sand bunker. The use of a wedge may entail a modified swing by the golfer, unless a full fairway shot requiring a normal, full swing is appropriate for the distance to the green. A significant design element in these wedges is the particular scoreline pattern on the front striking face of the club head, which is used to produce high spin rates.
One conventional design for a wedge-type golf club head includes an upper part that has a constant thickness, i.e., like a blade, and a lower part that is uniformly triangular in cross-section at the rear of the head. This provides a relatively low mass concentration, which combines with the high loft angle to aid the golfer in getting the club head under the golf ball, particularly in sand or tall, rough grass areas. The overall mass distribution results in a hard feeling upon contact with a golf ball that is unpleasant to many golfers. Generally, it is desirable for wedges to have a xe2x80x9csoftxe2x80x9d feel so that the golfer has feedback on the appropriate swing and contact with the ball in order to achieve the desired ball travel distance.
Other wedge designs remove some mass from the rear of the head at the toe area and another amount of mass from the heel area, to create two pockets or recesses. This forms a central bar at the rear of the club head. In one such design, the toe and heel end masses and the central bar extend to an upper position, toward the topline, at the rear of the club head. The increase in thickness of the central bar relative to the upper part of the club head is limited in order not to substantially increase the head""s weight. Another such wedge design has minimal amounts of mass removed from the toe and/or heel areas, so as to form a more cosmetic feature that does not differ substantially from the previous, conventional design. In both recess designs, a higher positioned mass at the rear tends to stiffen the club head.
Yet another such wedge recess design includes a high central bar at the rear of the club head coupled with a very low mass concentrated substantially horizontally above the sole of the club head. The central bar is used to add mass at a point of impact, and extends to nearly the top edge. Again, in order to minimize added mass, the central bar is not substantially thicker than the upper part of the club head. This design also tends to undesirably stiffen the impact area of the face and allows undesirable lateral vibration of the club head.
A somewhat opposite wedge design includes a U-shaped rib at the rear of the club head that extends from the heel end to the toe end. The rib eliminates the central bar and includes toe and heel masses that extend to nearly the top edge of the club head. However, the golf ball impacts a thinner club face at the center portion and, as a result, the club head may not impart the desired initial velocity or spin rate to the golf ball and may also produce an unpleasant feeling or vibration to the golfer.
The present invention provides an iron-type golf club head that has enhanced flexibility and selectively increased stiffness for improved performance and feel. The club head provides relative stiffness in a lower portion of the head, varying from heel to toe, combined with a reduced stiffness in an upper portion of the head, to provide improved vibration characteristics.
More particularly, the golf club head of the invention has a body having a planar upper portion and a rearwardly extending lower portion, the upper portion having a top edge and a substantially constant thickness, and the lower portion having a bottom edge. A front surface of the lower portion and a front surface of the upper portion together form a substantially planar striking face having a loft angle measured from a vertical axis. A rear side of the lower portion has at least a first recess adjacent to a toe end and at least a second recess adjacent to a heel end. A lateral axis at the junction of the upper and lower portions of the body extends from the toe end to the heel end, with a reference point being defined at a mid portion of the lateral axis, between about 50% and about 75% of the height of the striking face, measured from the bottom edge to the top edge. This reference point is located less than about 70% of the face height if the loft angle is less than about 56 degrees. A central axis is defined substantially parallel to the lateral axis, at approximately 50% of the face height.
Further, the first recess has a first volume and the second recess has a second volume, both recesses extending downwardly at least to the central axis. The portions of the body that define the first and second recesses each have a stiffness approximately the same as the stiffness of the upper portion, while the remainder of the lower portion has a stiffness at least 50% greater than the stiffness of the upper portion. A central region of the lower portion, located below the reference point, has a maximum stiffness that is at least about 20 times the stiffness of the upper portion. Regions located below the first and second recesses each have a maximum stiffness at least about 10 times the stiffness of the upper portion. A stiffness zone is located within the central region, at the central axis and extending halfway toward the lateral axis, between the first and second recesses, at least about 10% of the length of the striking face. A relative stiffness thereby is established between the central region and the upper portion and between the central region and the first and second recesses.